fix: various security fixes (#38406)

Addresses a batch of privately reported security issues, grouped by
area:

- **SSRF** - migration PR-patch/asset fetches, OAuth2 avatar & OpenID
discovery, pull-mirror URL re-validation, and the outbound proxy path.
- **Access-token scope** - prevent scope escalation on token creation;
keep public-only tokens confined (feeds, packages, Actions listings,
star/watch lists, limited/private owners).
- **Access control / disclosure** - go-get default-branch leak, webhook
authorization-header leak, watch clearing on private transitions,
label/attachment scoping.
- **Denial of service** - input bounds for npm dist-tags, Debian control
files, Arch file lists, and SSH keys.

### 📌 Attention for site admins

Not breaking - existing configs keep working - but two changes are worth
a look:

- **New SSRF protection** Outbound requests (migrations, OAuth2 avatars,
OpenID discovery, pull mirrors, proxy path) are now validated against
the allow/block host lists. If your instance legitimately reaches
internal hosts, you may need to add them to
`[security].ALLOWED_HOST_LIST` (and the relevant `ALLOW_LOCALNETWORKS`
settings).
- **Deprecation** `[webhook].ALLOWED_HOST_LIST` is deprecated and will
be removed in a future release. Use `[security].ALLOWED_HOST_LIST`
instead; the old key still works for now.

---------

Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

services/actions/task_test.go

@@ -7,6 +7,8 @@ import (
 	"testing"
 
 	actions_model "gitea.dev/models/actions"
+	"gitea.dev/models/db"
+	"gitea.dev/models/unittest"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -32,3 +34,41 @@ func TestTryPickTaskThrottled(t *testing.T) {
 	assert.False(t, ok)
 	assert.True(t, throttled)
 }
+
+// TestReleaseTaskForRunnerCleanup verifies the cleanup used by PickTask releases a claimed task through a
+// fresh context. PickTask reaches this path when the request context is already canceled, and on
+// PostgreSQL/MySQL a DB transaction on a canceled context fails immediately; reusing it would strand the
+// claimed job in running state, so the cleanup must not use the request context.
+func TestReleaseTaskForRunnerCleanup(t *testing.T) {
+	require.NoError(t, unittest.PrepareTestDatabase())
+
+	run := &actions_model.ActionRun{
+		Title: "cleanup-run", RepoID: 1, OwnerID: 2, WorkflowID: "test.yaml",
+		TriggerUserID: 2, Ref: "refs/heads/main",
+		CommitSHA: "c2d72f548424103f01ee1dc02889c1e2bff816b0", Event: "push", TriggerEvent: "push",
+		Status: actions_model.StatusWaiting,
+	}
+	require.NoError(t, db.Insert(t.Context(), run))
+	job := &actions_model.ActionRunJob{
+		RunID: run.ID, RepoID: run.RepoID, OwnerID: run.OwnerID, CommitSHA: run.CommitSHA,
+		Name: "cleanup-job", Attempt: 1, JobID: "cleanup-job", Status: actions_model.StatusWaiting,
+		RunsOn:          []string{"ubuntu-latest"},
+		WorkflowPayload: []byte("on: push\njobs:\n  cleanup-job:\n    runs-on: ubuntu-latest\n    steps:\n      - run: echo hi\n"),
+	}
+	require.NoError(t, db.Insert(t.Context(), job))
+	runner := &actions_model.ActionRunner{Name: "cleanup-runner", AgentLabels: []string{"ubuntu-latest"}}
+	runner.GenerateAndFillToken()
+	require.NoError(t, db.Insert(t.Context(), runner))
+
+	task, ok, err := actions_model.CreateTaskForRunner(t.Context(), runner)
+	require.NoError(t, err)
+	require.True(t, ok)
+	require.Equal(t, actions_model.StatusRunning, unittest.AssertExistsAndLoadBean(t, &actions_model.ActionRunJob{ID: job.ID}).Status)
+
+	// the cleanup helper uses its own context, so the claimed job is returned to the waiting queue
+	releaseTaskForRunnerCleanup(task)
+	released := unittest.AssertExistsAndLoadBean(t, &actions_model.ActionRunJob{ID: job.ID})
+	assert.Equal(t, actions_model.StatusWaiting, released.Status)
+	assert.Zero(t, released.TaskID)
+	unittest.AssertNotExistsBean(t, &actions_model.ActionTask{ID: task.ID})
+}